1. Field of the Invention
The present invention relates to a data communication apparatus capable of sending and receiving image data of irregular size.
2. Related Background Art
As apparatuses of this type, facsimile apparatuses are known. Facsimile apparatuses for sending and receiving image data through a telephone line or a digital network have been recently used widely in companies and homes.
Most facsimile apparatuses transmit an original of a regular size determined by CCITT Recommendations. For example, if an original to be transmitted is A4 size and it is read at a reading resolution of 8.times.7.7 pel/mm, the original is read one line after another in units of 1728 bits in the main scan direction and thereafter it is transmitted.
As facsimile apparatuses are used more and more in homes, it can be expected that a handy scanner of a small size and low cost will be used as an image reader. The length in the main scan direction read with a small handy scanner is considerably smaller than the regular image data size (e.g., A4 paper size and 1728 bits at resolution of 8.times.7.7 ppi) determined by CCITT Recommendations.
Most facsimile apparatuses presently available in markets have as their recording paper sheets only roll-type regular size paper sheets. Accordingly, if image data read with a small handy scanner is transmitted as a regular size image with the blank bit portion being transmitted as white, a wasteful large blank portion is received at a receiving side.
Furthermore, with respect to facsimile apparatuses having a function to store a large capacity of transmitted or received images, each time stored image data is read out for search by scroll using a display unit the resolution of the image data is converted into so as to match the resolution of the display unit.
Since the stored image data is converted and outputted to match the resolution of the display unit when a request of displaying the image data is instructed, it takes a lot of time to read out the image data and convert the resolution. Therefore, speeding up of such processes requires a large scale of hardware so that there is a limit in speeding up.
The technique regarding transmission of an irregular size image data is disclosed in U.S. Pat. No. 4,712,139 and U.S. patent application Ser. No. 049,948 filed on Mar. 29, 1988, abandoned. However, the technique for solving the above is not know as yet.